1. Field of the Invention
This invention relates generally to the field of digital to analog converters (DAC) for communications applications. More particularly, the invention provides a DAC with integral intersymbol interference (ISI) cancellation based on the inherent characteristics of dynamic element matching (DEM).
2. Description of Related Art
DACs for communications systems typically employ an oversampling architecture with dynamic element matching (DEM) for improve linearity {noise reduction}. DEM is the preferred scrambling technique used to overcome the harmonic distortion that would be present in thermometer style decoding if assignment of each particular bit was active only during a particular input code. With DEM, correlation between the bit output from the scrambler and the particular input value is eliminated. Errors which would be introduced by bit-weights in the DAC are therefore de-correlated from the signal.
Even with DEM, dynamic non-linearity problems exist which impact the performance of the DAC. Extensive work in the prior art for return to zero (RZ) architectures to reduce this dynamic non-linearity has been done. However, such RZ architectures add significant complexity to the overall architecture design and may introduce further non-linearity {noise} issues associated with RZ wave shape itself.
It is therefore desirable to reduce ISI without added circuit complexity and the additional noise creation inherent in RZ architectures for DACs.